The present invention relates to a process for the production of 3-functionalized propyl silanes.
It is known, that hydrogen silanes can be reacted with, for example, allyl chloride in the presence of homogeneous or heterogeneous platinum catalysts to produce 3-chloropropyl silanes. This reaction is generally known as hydrosilylation (see for example equation I).
Clxe2x80x94CH2xe2x80x94CHxe2x95x90CH2+HSiCl3xe2x80x94Clxe2x80x94CH2xe2x80x94CH2xe2x80x94CH2xe2x80x94SiCl3xe2x80x83xe2x80x83(I)
If soluble platinum compounds, in the simplest case, for example, H2PtCl6xc3x976 H2O, are used (cf. DE-OS 28 51 456, CS-PS 176 910, U.S. Pat. No. 4,292,433, U.S. Pat. No. 4,292,434, DE-AS 11 87 240, DE-PS 11 65 028) this is called homogenous hydrosilylation. With heterogeneous hydrosilylation, elemental platinum or platinum compounds on a carrier are used (cf. U.S. Pat. No. 2,637,738, DE-PS 20 12 229, DE-PS 28 15 316).
Furthermore, it is known that when reacting, for example, allyl chloride with hydrogen silanes to produce 3-chloropropyl silanes, some of the allyl chloride used reacts with the hydrogen silane in a secondary reaction producing propene and the chlorosilane corresponding to the particular hydrogen silane (see for example equation II).
Clxe2x80x94CH2xe2x80x94CHxe2x95x90CH2+HSiCl3xe2x86x92CH3xe2x80x94CHxe2x95x90CH2+SiCl4xe2x80x83xe2x80x83(II)
Thus, when reacting allyl chloride with trichlorosilane, for example, 25-30 mol % of the allyl chloride attaining reaction is converted by this secondary reaction into propene. This produces an equivalent quantity of silicon tetrachloride.
The mol ratio of chloropropylsilane to silicon tetrachloride produced is a measure of the selectivity of the reaction and typically achieves values of 2.33:1 (70% yield in relation to allyl chloride) and 3:1 (75% yield).
Furthermore it is known that the formation of propene can be reduced by a special reaction method using pressure apparatus. The result of this method is that the propene further reacts quantitatively with the hydrogen silane to produce propyl silanes. Even with the reactions carried out in the usual way, under normal pressure, a considerable quantity of the propene originating from the secondary reaction is converted to the corresponding propyl silanes in a further secondary reaction with hydrogen silane (cf. also DE 34 04 703 C) (see for example equation 3).
CH3xe2x80x94CHxe2x95x90CH2+HSiCl3xe2x86x92CH3xe2x80x94CH2xe2x80x94CH2xe2x80x94SiCl3xe2x80x83xe2x80x83(III)
Thus, for example, a heterogeneous catalytic reaction in a commercial apparatus of allyl chloride and trichlorosilane in an acid filled with platinated active carbon produces up to 230 kg propyl trichlorosilane per 1000 kg 3-chloropropyl trichlorosilane. This requires an excess of approx. 28% trichlorosilane in relation to the quantity of trichlorosilane incorporated into the end product (cf. also DE 41 19 944 A1).
The known processes have the disadvantage that, firstly, there is a need for additional hydrogen silane and secondly, the unwanted propyl silanes are not easy to separate off. In addition to this, there are few applications for these compounds, which must therefore be disposed of at great cost.
An object of the present invention is therefore to find a process for the production of 3-position functionalized propyl silanes, which does not have these disadvantages.
The above and other objects of the invention can be achieved by a process for the production of 3-functionalized propyl silanes by the addition of allyl compounds of the general formula I
H2Cxe2x95x90CH xe2x80x94CH2Xxe2x80x83xe2x80x83(I)
wherein X can be Cl, Br, I, F, CN, SCN, SH, SR, OH, NRR1 and OR, and R and R1, both independently of each other, mean (C1-C6)alkyl or (C3-C7)alkyl, to silanes of the formula II
R2R3R4SiHxe2x80x83xe2x80x83(II),
wherein R2, R3, R4, all independently of each other, are hydrogen, halogen, (C1-C6)alkyl, (C1-C6)haloalkyl, (C3-C6)allyl, (C1-C4)alkoxy, phenyl, aryl or aralkyl,
at reaction temperatures of 0xc2x0 C. to 200xc2x0 C. and pressures of 800 mbar to 25 bar and in the presence of a platinum catalyst,
characterised in that the silane (II) used is brought into contact with the catalyst in a 3- to 100-fold molar excess in relation to the propene compound (I).
Surprisingly, it is found that the formation of by-products is suppressed if large excesses of hydrogen silane are present on the catalyst. Then, in the reaction of allyl chloride with trichlorosilane for example, the selectivity normally achieved of 74% Cl-PTS yield in relation to allyl chloride can be increased to 85%. At the same time, the quantity of the by-product propyl trichlorosilane formed is reduced by 50% and the need for trichlorosilane educts by 20%, and allyl chloride by 12%.
A halogen, in particular chlorine, can preferably represent X.
The process can be carried out at normal pressure, excess pressure or reduced pressure. Pressures of 800 mbar to 10 bar are preferred. A pressure of 800 mbar to 6 bar is particularly suitable.